There are various kinds of media which store data. Such media include, for instance, a memory device based on a client/server model. A memory system, which is composed of a memory device and a host device based on the client/server model, is different from other memory systems in some points. For example, the assignment of roles to the memory device and host device based on the client/server model is different from the assignment of roles to a memory device and a host device which are not based on the client/server model. Accordingly, the contents of communications between the host device and memory device differ between the system based on the client/server model and the system not based on the client/server model.
In some cases, a memory system accords with a specific standard. An example of the memory system based on the client/server model is a UFS (Universal Flash Storage) memory device and host device. As regards points specified in the standard, the memory system must accord with specifications. However, there are points which are not specified in the standard, and a designer of the memory system can decide on such points. Such items with a degree of freedom should be determined so that desirable capabilities may be realized in a manner to adapt to the characteristics of the memory system. There has been a demand that a memory device, which can realize higher capabilities, be provided by making proper decisions on such matters with a degree of freedom.